7. Nearly 30% of the solar radiations return back to the space without contributing anything to the earth’s surface temperature. This amount of radiation is known as—
a) black body b) tropopause
c) earth’s albedo d) mesopause

9. The first general election in India on the basis of adult suffrage was held during the year
a) 1951-52
b) 1953-54
c) 1949-50
d) 1947-48

10. Consider the following state- ments :

1. Ozone is mostly found in the stratosphere.
2. Ozone layer lies 55-75 km above the surface of the Earth.
3. Ozone absorbs ultraviolet radiation from the Sun.
4. Ozone layer has no significance for life on the Earth.
Which of the statements given above are correct ?
a) 1 and 2
b) 1 and 3
c) 2 and 3
d) 3 and 4

Answers :

1. C . Antibodies, also called immunoglobulins, are large Y-shaped proteins which function to identify and help remove foreign antigens or targets such as viruses and bacteria.
Antibodies are produced by the immune system in response to the presence of an antigen. Antigens are large molecules, usually proteins, on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, and foreign particles. Any substance capable of triggering an immune response is called an antigen.

2. D . Silk is a protein fiber made by silk worms and is the only natural fiber that is a filament fiber. The first country to manufacture silk fabric was China. Silk can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and produced by certain insect larvae to form cocoons.

3. C . Cytokinins are a group of plant hormones which acts synergistically with auxins to promote cell division. Cytokinins can retard ageing of plant organs by controlling protein synthesis and mobilization of resources.

4. B. The lipids are a heterogenous group of substances found in plant and animal tissues, which share the property of being relatively insoluble in water, and soluble in organic solvents, such as ether, choloroform and benzene. Lipids are important sources of metabolic energy (ATP). In fact, the lipids are the most energy rich of all classes of nutrients. Lipids serve as biological carriers for the absorption of the fat soluble vitamins A, D, E and K.

5. B. Enzymes are very efficient catalysts for biochemical reactions. They speed up reactions by providing an alternative reaction pathway of lower activation energy. Most enzymes are proteins. greatly accelerating both the rate and specificity of metabolic chemical reactions, from the digestion of food to the synthesis of DNA.

6. A . The Sun emits a tremendous amount of energy, in the form of electromagnetic radiation, into space.The average amount of the sun’s radiation that penetrates the atmosphere and reaches the earth is 51% of the total incoming energy . Of the 49% that does not reach the earth, 30% is reflected back into space and 19% is absorbed by the atmosphere and clouds.

7. C . Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space. It is a measure of the reflectivity of the earth’s surface.Since 30% of the sun’s energy is reflected by the entire earth, the earth has an average albedo of .30 fresh snow has a high albedo of .95

8. A .

9. A . The first General Elections held from 25 October 1951 to 21 February 1952.

10. B. The ozone layer or ozone shield refers to a region of Earth’s stratosphere that absorbs most of the Sun’s UV radiation. It contains relatively high concentrations of ozone (O3). It is mainly located in the lower portion of the stratosphere from approximately 15 km to 35 km above Earth’s surface, though the thickness varies seasonally and geographically.

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